Switched full-duplex ethernet type communication network and implementation process for this network

ABSTRACT

A switched full-duplex Ethernet type communication network including at least one source subscriber equipment and at least one destination subscriber equipment connected to each other through at least one physical link through at least one switch and at least one virtual link, which is the conceptual representation of a link from a source equipment to at least one destination equipment. Each equipment transmitting Ethernet frames segregates between virtual links and allocation of a passband for each virtual link and multiplexes virtual links on the physical link output from this equipment. Each transmitted frame has a field that identifies the virtual link to which it belongs.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present patent document is a continuation of U.S. applicationSer. No. 10/287,912 filed on Nov. 4, 2002, and claims priority to Frenchpatent application FR 01 14263 filed Nov. 5, 2001, the entire contentsof each of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a switched full-duplex Ethernet typecommunication network, particularly in avionics.

[0004] 2. Description of the Related Art

[0005] The Ethernet network, which is the reference in the world ofcommunication networks, can be used to send data in digital form bypackets or “frames”, where a packet is defined as being a set of datasent in a single step on the network.

[0006] In an Ethernet network, the data in each packet are notinterpreted. The network carries the data without understanding theirmeaning. A packet is composed of two types of data, network data thatare used to route the packet to its correct destination, and useful datawhich comprise the “useful load” in the packet.

[0007] An Ethernet network is composed of different equipment that issubscribed to the network, and connected to each other through acommunication means formed of active equipment called switches, whichperform three functions:

[0008] connect network subscribers in point to point mode throughphysical links, which are physical supports for messages to betransferred, for example twisted pair cables,

[0009] route (switch) packets sent by source equipment to one or moredestination equipment,

[0010] check the integrity and the format of the Ethernet packet.

[0011]FIG. 1 illustrates an Ethernet network composed of two switches 11interconnected to each other and each connected to three items ofsubscriber equipment 12 in point to point mode.

[0012] Operation of such a network is simple. Each network subscribercan send packets in digital form at any time towards one or severalother subscribers. When a switch receives the packets, the “networkinformation” data are analyzed to determine the destination equipment.The packets are then switched towards this equipment.

[0013] In the “switched full-duplex Ethernet type network” expression:

[0014] the “full-duplex” term means that the subscriber can send andreceive packets at the same time on the same link,

[0015] the “switched” term means that the packets are switched inswitches on appropriate outputs.

[0016] For example, this network may be a 100 Mbits/s switchedfull-duplex type network on twisted pair; the term “twisted pair” meansthat connections between the equipment and the switches are composed oftwo pairs of cables, each pair being twisted; the term 100 Mbits/ssimply means the transmission or reception speed of packets on thenetwork.

[0017] The Ethernet technology imposes:

[0018] a minimum size and a maximum size on the packets,

[0019] an identification of the source and/or the destination(s) in eachpacket,

[0020] a CRC (“Cyclic Redundancy Check”) that checks the integrity ofthe transported data.

[0021] At the present time, in the civil aeronautics field, dataexchanges between the various onboard computers are based on the use ofthe ARINC 429 aeronautical standard.

[0022] However, the switched full-duplex Ethernet network is frequentlyused in industry. The emergence of new communication technologies showsthat this type of network is an open and standard solution (IEEEstandard 802.3) with a considerable potential for development as a localnetwork. But this type of solution does not provide any means ofguaranteeing segregation and transfer performances (in terms of networkaccess, latency, etc.) necessary for avionics applications.

SUMMARY OF THE INVENTION

[0023] The purpose of this invention is to propose a switchedfull-duplex Ethernet type network, which guarantees data segregation anda limit to data transfer time, to enable application in avionics.

[0024] The invention relates to a switched full-duplex Ethernet typenetwork comprising at least one source subscriber equipment and at leastone destination subscriber equipment connected to each other through atleast one physical link through at least one switch and through at leastone virtual link which is the conceptual representation of a link from asource equipment to at least one destination equipment, characterised inthat each source equipment transmitting Ethernet frames comprises:

[0025] means of segregation between virtual links and allocation of apassband for each virtual link,

[0026] means of multiplexing virtual links on the physical link outputfrom this equipment, each transmitted frame having a field thatidentifies the virtual link to which it belongs.

[0027] Advantageously, each destination equipment comprises means ofsubscribing to at least one virtual link in reception and achievingsegregation between virtual links as far as the application.

[0028] Advantageously, each switch comprises incoming passband controlmeans for each virtual link. It uses a static configuration table toknow which virtual links it needs to switch, and the allowable number ofpackets for a virtual link. It comprises:

[0029] means of separately configuring each input port in order toindicate the output ports towards which each received Ethernet framemust be directed as a function of the virtual link identifier,

[0030] means of monitoring the flow of Ethernet frames associated witheach virtual link that passes through the switch,

[0031] means of reformatting the flow in each virtual link,

[0032] means of multiplexing flows in virtual links on each output port.

[0033] In one example embodiment, each switch comprises the following insequence:

[0034] an input port,

[0035] flow control means,

[0036] a switching motor supporting multidestination transfers,

[0037] flow control means,

[0038] flow reformatting means,

[0039] virtual link multiplexing means,

[0040] an output port.

[0041] Advantageously, a virtual link is characterized by:

[0042] a transfer direction, the virtual link being single directional,

[0043] a single transmitter subscriber: in this case the equipment,

[0044] one or several subscribers in reception: in this case theequipment,

[0045] a fixed passband (maximum number of packets per second and theirsize),

[0046] a maximum guaranteed time for transfer of packets from a sourceequipment to a destination equipment, regardless of the behaviour of therest of the network, each virtual link having its own transfer time,

[0047] a path fixed on the network,

[0048] an unique identifier.

[0049] In one advantageous embodiment, network redundancy is achieved bydoubling up the network, each subscriber having a connection to each ofthe two networks.

[0050] The invention also relates to a process for implementation of aswitched full-duplex Ethernet type communication network comprisingsource and destination subscriber equipment connected to each otherthrough at least one physical link through at least one switch andthrough at least one virtual link that is the conceptual representationof a link from a source equipment to at least one destination equipment,characterized in that in a transmission service, an application isallowed to access virtual links in transmission, this service being usedto multiplex virtual links to the physical link through an Ethernetinterface, and to send packets for each virtual link as a function ofthe passband allocated to the virtual link. In a reception service, thepackets are decoded, it is checked that their format is correct anduseful data are made available to applications. In a passband protectionservice in the switch, the time characteristics of the packets arechecked for each incoming virtual link, and if the allowablecharacteristics are exceeded, packets are destroyed to prevent a failureat a transmitter or a virtual link from compromising traffic in othervirtual links output from this switch.

[0051] Advantageously, in one network redundancy service at subscriberlevel, a packet is sent and received in two virtual links in order toset up network redundancy, duplication of the network that istransparent for applications to guard against a failure in a switch oran interface.

[0052] Advantageously, in a “sampling” service, the destination terminalonly presents the last received value to the user, and in this servicethe last value is systematically overwritten by the new received packet.In a “queuing” service, the destination equipment presents all data thatit receives to the user, this service making it possible to:

[0053] send information that the addressee does not want to lose,

[0054] send data larger than the maximum packet size on the virtuallink, the transmission service then breaking this data down intopackets, and the reception service putting the data together again tomake them available to the receiving application.

[0055] In a “file transfer” service, a data file is transferred and thetransmission service breaks this file down into packets which are thentransmitted sequentially, and the reception service recreates this file.

[0056] Advantageously, a passband and an inter-packet time are assignedfor each virtual link.

[0057] In one advantageous embodiment, a subscriber in reception refinesthe selection of packets on the same virtual link using the networkaddressing information contained in the packet.

[0058] Advantageously, data integrity is achieved on each packet by aCRC that carries out a calculation to validate data transmitted in thepacket, each packet is verified at each equipment entry on the network,and every bad packet is destroyed so that it is not used in order torelease the passband and thus avoid uselessly creating congestion at theswitches.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] A more complete appreciation of the present invention and many ofthe attendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0060]FIG. 1 illustrates an Ethernet network according to known art,

[0061]FIG. 2 illustrates the concept of a virtual link in an Ethernetnetwork according to the invention,

[0062]FIG. 3 illustrates an Ethernet network in which several virtuallinks according to the invention are shown,

[0063]FIGS. 4A shows the composition of a transmission equipment, andFIG. 4B shows the composition of a reception equipment, for the networkaccording to the invention,

[0064]FIG. 5 illustrates the different component elements of a switch inthe network according to the invention,

[0065]FIGS. 6 and 7 illustrate different services used in the networkaccording to the invention,

[0066]FIG. 8 illustrates the location of “sampling”, “queuing” and “filetransfer” services with respect to the application and virtual linkservices as illustrated in FIGS. 6 and 7, in the network according tothe invention,

[0067]FIG. 9 illustrates two examples of packet distributions in asequence,

[0068]FIG. 10 illustrates the filtering function in a virtual link inreception according to the invention,

[0069]FIG. 11 illustrates an example of a transfer time for a virtuallink VL1 according to the invention,

[0070]FIG. 12 illustrates an example verification of the packet in thevirtual link VL1 in FIG. 11 according to the invention,

[0071]FIG. 13 illustrates the decomposition of the useful load of apacket in an example embodiment of the network according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0072] The switched full-duplex Ethernet network according to theinvention uses the virtual link concept to limit the end to end transfertime, in other words from a source equipment to one (or several itemsof) destination equipment.

Concept of Virtual Link

[0073] This virtual link (VL) concept provides means of isolating datatransfers between a source equipment 13 and destination equipment 14. Avirtual link VL is seen as a “pipe” on the network, as illustrated inFIG. 2.

[0074] A virtual link VL is characterized by:

[0075] a transfer direction, the virtual link being single directional,

[0076] a single source equipment 13,

[0077] one (or several items of) destination equipment 14,

[0078] a fixed passband (maximum number of packets and their size persecond),

[0079] a maximum guaranteed time for transfer of packets from a sourceequipment 13 to a destination equipment 14, regardless of the behaviorof the rest of the network, each virtual link having its own transfertime,

[0080] a path fixed on the network,

[0081] an unique identifier.

[0082] A network subscriber may comprise several virtual links VL1, VL2,VL3, as shown in FIG. 3. We have:

[0083] a virtual link VL1 from equipment 21 to equipment 23, 24 and 25,

[0084] a virtual link VL2 from equipment 21 to equipment 22 and 23,

[0085] a virtual link VL3 from equipment 23 to equipment 22,

[0086] When equipment 21 wants to send a packet to equipment 23, 24 and25, it sends a packet on the virtual link VL1. When it wants to send apacket to equipment 22 and 23, it sends a packet on the virtual linkVL2.

[0087] The difference between virtual links VL1 and VL2 is identified bythe destination identifier in the packet. On the network, the virtuallink to which a packet belongs is determined by the identifier of thevirtual link in the packet.

[0088] A switch uses a static configuration table to determine thevirtual links that it is required to switch, and the allowable number ofpackets for a virtual link.

[0089] The virtual link concept is a means of fixing communicationsbetween equipment by configuring routes and passbands allocated to thevirtual links. Thus, the flow formed by a virtual link is sure to be notdisturbed by other flows sharing the same physical links all along itsroute in the network.

[0090] Furthermore, the virtual link concept enables central flowmanagement, to make sure that the sum of the passbands allocated tovirtual links on the same physical link does not exceed the capacitiesof the technology of this physical link. In the above example, the sumof the passbands of virtual links VL1 and VL2 must be less than thetransmission capacity of the physical link from equipment 21.

[0091] In the network according to the invention, each equipmentcomprises:

[0092] means 32 that define virtual links in transmission and thatallocate passbands by controlling segregations,

[0093] means 33 that sequence accesses of virtual links to the physicallink, in transmission,

[0094] means 34 that make it possible to subscribe to one or severalvirtual links in reception, and that enable segregation between virtuallinks as far as the application.

[0095]FIGS. 4A and 4B represent these means in transmission and inreception respectively, between an application 30 and a physical layerEthernet controller 31; the complete assembly of means 32 and 33 forminga communication stack 35 and the means 34 forming a communication stack36.

[0096] In the network according to the invention, each switch comprises:

[0097] means of separately configuring each input port in order toindicate the output ports towards which each received Ethernet framemust be directed as a function of the virtual link identifier,

[0098] means of monitoring the flow of Ethernet frames associated witheach virtual link that passes through the switch,

[0099] means of reformatting the flow in each virtual link(re-separation of frames for each virtual link),

[0100] means of multiplexing flows in virtual links on each output port.

[0101] Therefore as illustrated in FIG. 5, this switch includes thefollowing in sequence:

[0102] an input port 41,

[0103] flow control means 42,

[0104] a switching motor supporting multidestination transfers 43,

[0105] flow control means 44,

[0106] flow reformatting means 45,

[0107] means of multiplexing the virtual links 46,

[0108] an output port 47.

[0109] Thus, as illustrated in FIG. 6, the network according to theinvention is characterized by the implementation of several services ormeans in each of the subscriber equipment 50:

[0110] a transmission service, the role of which is to enable anapplication 52 to access virtual links in transmission. This servicemultiplexes virtual links to the physical link 53 through an Ethernetinterface 54, and for each virtual link sends packet as a function ofthe passband allocated to the virtual link.

[0111] A reception service 55 that decodes the packets, verifies thattheir format is good and makes useful data available to applications.

[0112] In these transmission and reception services, the virtual linkmay be represented as being a queue, as seen by the application.

[0113] Other protection services are used to guard against some networkfailures:

[0114] A passband protection service in the switch, which verifies thetime characteristics of packets (separation between packets, theconsumed passband), for each incoming virtual link. If the allowablecharacteristics are exceeded, the packets will simply be destroyed toprevent a failure in a transmitter or a virtual link from compromisingtraffic in other virtual links starting from this switch.

[0115] A network redundancy service 60 at subscriber level, that enablestransmission and reception of a packet on two virtual links in order toimplement a network redundancy. Duplication of the network, which istransparent for applications, thus provides protection against a failurein a switch or an interface (but it does not replace redundancy atsystem level). As shown in FIG. 7, there are also the transmission andreception services 51 and 55 in FIG. 6, and a network transmissionreception redundancy service 60 to which is connected to a firstEthernet interface 61 and to a second Ethernet interface 62.

Transmission and Reception Modes

[0116] The communication interface may supply three additional servicesto subscriber level applications:

[0117] “Sampling”: the destination equipment only presents the lastreceived value to the user. In reception, the last value issystematically overwritten by the new received packet. This service issuitable for receiving periodic information.

[0118] “Queuing”: destination equipment presents all data that itreceives to the user, even if the receiver does not read them quicklyenough. This service is useful for:

[0119] sending information that the addressee does not want to lose (allpackets will be read),

[0120] sending data larger than the maximum size of the packet on thevirtual link. The transmission service then breaks these data down intopackets. The reception service reformats the data to make them availableto the receiving application.

[0121] “File transfer”: this service transfers a data file.

[0122] The transmission service breaks it down into packets which arethen transmitted sequentially. The reception service reconstructs thefile. It is also capable of restarting on error (for example in the caseof a data download).

[0123]FIG. 8 illustrates the location of these services with respect toapplications and services on virtual links, using the same references asin FIG. 6.

Transmission of Packets on a Virtual Link

[0124] The invention does not only relate to the definition of virtuallinks that are used in equipment to send and receive data. It alsorelates to a particular use of the allocated passband, and sub-filteringfunctions on reception in a virtual link.

[0125] 1) The Allocated Passband and Inter-packet Time

[0126] The allocated passband is defined as being the number of packetssent per second and the size of each packet. But this definition isincomplete because a passband does not give the distribution of thesepackets in time. It is also necessary to specify the minimum time to berespected between two packets. This minimum inter-packet time (IPT)gives the maximum passband of the virtual link for a given packet size.

[0127]FIG. 9 thus illustrates two example packet distributions in asequence 70:

[0128] a distribution 71 of 10 packets separated by 1 bit,

[0129] a uniform distribution 72 of 10 packets. The fact of indicatingthat the minimum inter-packet time is 100 ms gives the maximum trafficenvelope on this virtual link, and the passband can be deduced from thepacket size using the following formula:$\frac{{Packet}\quad {Size}}{{Minimum}\quad {inter}\text{-}{packet}\quad {time}} = {{passband}\quad {of}\quad {virtual}\quad {link}}$

[0130] The assignment of a passband (PB) and an inter-packet time (IPT)for a virtual link does not mean that the packets will systematically betransmitted on the virtual link every IPT and occupy the entireallocated passband. These packets will only be sent on the virtual linkwhen a subscriber application makes them available to the transmissionin this virtual link.

[0131] 2) The Filter Function in a Virtual Link in Reception

[0132] On the same virtual link, a subscriber in reception can refinethe selection of packets using network addressing information containedin the packet. This filter mode which uses a virtual sub-links conceptgives greater flexibility for the definition and use of virtual links byavoiding the creation of specific virtual links.

[0133]FIG. 10 gives an example of a virtual link that supports a streamof three types of packets (a, b and c). Each subscriber can filter (75)the packets according to its needs (subscriber A1-packet a; subscriberA2-packet b; and subscriber A3-packet C).

Performances of the Network According to the Invention

[0134] The performances of the network according to the invention can bebroken down in four ways:

[0135] data integrity,

[0136] network availability,

[0137] network determinism,

[0138] end to end routing of data.

[0139] 1) Data Integrity

[0140] Data integrity is achieved on each packet by a CRC (CyclicRedundancy Check) that enables a calculation to validate datatransmitted in the packet. The CRC is located at the end of the packetand it corresponds to all bits in the packet (network information plususeful information).

[0141] In the network a packet is verified at each equipment entry tothe network, so that every bad packet can be destroyed so that it cannotbe used, in order to release the passband and to avoid unnecessarilyoverloading the switches.

[0142] 2) Network Availability

[0143] The network is shared by several systems for communications.Therefore its availability has a non-negligible impact on the globalavailability.

[0144] This availability is increased by network redundancy, thatconsists of doubling up the network, with each subscriber having aconnection to each of the two networks, and one of the two packets beingselected on reception.

[0145] This network redundancy enables operation even if a switch orseveral links are defective.

[0146] 3) Network Determinism

[0147] The network is a deterministic network. This means that anypacket belonging to a virtual link for an allocated passband is sure ofaccessing the network and being transmitted to receiving equipment for alimited latency time (maximum packet transit time).

[0148] For a virtual link, the maximum latency calculation is given bythe following formula:

Latency time of a virtual link=Ta _(E) +TTE+(NS×TTS)+TTR+TA _(R)

[0149] Where

[0150] TTE: crossing time through the communication stack intransmission, corresponding to the time necessary to form packets in thecommunication services. This time is identical for all virtual links andis dependent on the hardware supporting the application.

[0151] TA_(E): transmission access time. The allocated passband is givenin the form of a maximum passband and a minimum time between twoconsecutive packets (inter-packet time IPT). Since packets are sent in avirtual link asynchronously with regard to the application, if a packethas just been sent, it will be necessary to wait for a time IPT beforeaccessing the network: thus TA_(E)≦IPT in all cases.

[0152] NS: number of switches through which the virtual link passes,

[0153] TTS: maximum time for a packet to pass through a switch,

[0154] TTR: crossing time in reception through the communication stack,corresponding to the time TTE but in reception. This time includes thepacket reception time by the services. It is identical for all virtuallinks, and it depends on the hardware supporting the application.

[0155] TA_(R): access time in reception. When a subscriber receives apacket, it is made available to the application through a “mail box”. Asa maximum, TA_(R)=IPT.

[0156] The times TA_(E) and TA_(R) are a result of the asynchronismbetween the applications and the network in transmission and reception.

[0157] A first estimate will give the following maximum values for apacket transfer time, independently of the virtual links:

[0158] TTE=0.5 ms

[0159] TTR=0.5 ms

[0160] TTS=1 ms.

[0161] In the example illustrated in FIG. 11, in which the references inFIG. 2 are repeated, we have:

[0162] For the virtual link VL1 from equipment 13 to equipment 14through two switches 11, if the time IPT=5 ms and the read interval=1ms, we have:

[0163] TA_(E)=5 ms

[0164] NS=2

[0165] TA_(R)=1 ms

[0166] Latency time for a virtual link=9 ms.

[0167] 4) End to End Routing of Data

[0168] The network according to the invention creates a single end toend route using virtual links, for each packet.

[0169] At each subscriber, each packet is assigned on transmission to avirtual link predefined by configuration. This packet has an addressingpart that contains the identification of the virtual link. Thisidentification is used for routing in the network.

[0170] In the routing of a packet, a service verifies if a packet isauthorized to pass through each switch at which the packet arrives.Similarly, on reception, a service checks if the packet belongs to avirtual link authorized in reception. If not, the packet is destroyed.

[0171]FIG. 12 illustrates an example verification of a packet in thevirtual link VL1 in FIG. 10. This check takes place at points 80.

Example Embodiment of the Network According to the Invention in Avionics

[0172] In this example embodiment, several characteristics of thenetwork according to the invention have been specified, in order tosimplify and standardize the use of this network in avionics.

Characteristics of Virtual Links

[0173] 1) Number of Virtual Links

[0174] Three subscriber classes are defined, depending on the number ofvirtual links in transmission and reception:

[0175] large consumer subscriber,

[0176] medium consumer subscriber,

[0177] small consumer subscriber.

[0178] This type of distribution is given in table 1 at the end of thedescription.

[0179] 2) Passband in Virtual Links

[0180] Each virtual link has an allocated passband that is given by theminimum inter-packet time (IPT) and the packet size. The IPT is given bythe following formula:

IPT=1 ms×2^(k) where K is an integer from 0 to 7;

[0181] which gives either 1 ms, 2 ms, 4 ms, 8 ms, 16 ms, 32 ms, 64 ms,or 128 ms.

[0182] By definition, four maximum packet sizes have been defined foreach virtual link, namely 16 bytes, 98 bytes, 226 bytes and 482 bytes.This size only indicates useful data for the packet, used byapplications directly. Network information data are also taken intoaccount for calculation of the passband.

[0183] In table 2 at the end of the description, the effective passbandson the network for a virtual link are given for each packet size (usefulload) and for each IPT time.

[0184] The required transmission passband for equipment on aircraft islow (<400 kbits/s). Thus, an upper bound in transmission is given whichis summarized by the rule that the sum of passbands of the virtual linksVL in transmission must be less than 5 Mbits/s. Thus, in transmission wecan have:

[0185] a subscriber with ten 16-byte virtual links at 2 ms (which gives3.36 Mbits/s), or

[0186] a subscriber with five 16-byte virtual links at 2 ms and ten226-bytes virtual links at 16 ms and one 226-byte virtual link at 4 ms(which gives 4.778 Mbits/s).

[0187] In order to allocate a passband to a virtual link, a real needhas to be identified in terms of data transmission frequency and volume.

[0188] Margins on the passband are given in two ways, either byduplication of the virtual link, or by an effective margin on thepassband of the virtual link. In the latter case, it is possible to:

[0189] allocate a useful size larger than necessary,

[0190] allocate a shorter time IPT, so that the packet transmissionfrequency can be increased, for example the number of packets per secondcan be doubled if the time IPT changes from 16 ms to 8 ms,

[0191] a combination of the useful size and the time IPT.

[0192] 3) Virtual Links Mode

[0193] Three transfer modes have been defined above, namely “sampling”,“queuing”, and “file transfer”. In order to facilitate the definitionsin the virtual links, each virtual link is used either in “sampling”mode or in “queuing” mode or in “file transfer” mode.

[0194] 4) Filtering

[0195] The possibility of filtering in a virtual link enables someequipment to avoid an excessive number of virtual links in transmissionand in reception (if the same transmitter). This means can be used togroup several virtual links into a single link and to define “virtualsub-links”, the packets being selected by network information containedin the packet. Filtering gives better flexibility on the use ofcommunication “pipes” and enables optimisation of their use.

Structure and Format of the Useful Load

[0196] The term “structure” specifies the arrangement of the useful load(data transmitted and received by applications) in the packet.

[0197] The term “format” specifies the type of data (integer, binary,etc.).

[0198] The Ethernet standard does not impose the packet structure andthe data format (unlike the ARINC 429 standard); however, the followingrules are respected in the example considered.

[0199] As illustrated in FIG. 13, the useful load comprises:

[0200] the functional validity (VF) valid for all data in the packet,

[0201] the data themselves, coded according to a standard format,

[0202] the arrangement of the data themselves shall be defined by commonagreement between the transmitter and the addressees.

[0203] 1) Functional Validity

[0204] The transmitter calculates the functional validity, and thereceiver or receivers use it to determine the degree of confidence to beassigned to the transmitted packet. The functional validity is coded inthe first four bytes of the packet.

[0205] The functional validity is the equivalent of “SSMs” used on theARINC 429 aeronautical standard. However, there are some majordifferences:

[0206] This functional validity is purely functional, in other words itonly reflects the state of data determined by the transmittingapplication, and not the state of resources that support it.

[0207] The functional validity may be equal to one of the followingvalues:

[0208] NO: “Normal Operation”

[0209] NCD: “No Computed Data”

[0210] FTF: “Functional Test”

[0211] The validity of the resources due to distanciation betweenapplication and resource cannot be generated by the functional validity.

[0212] 2) Data Format

[0213] Data are coded in a predefined format, in order to standardizeexchanges. This format is as similar as possible to the “computer”format manipulated by compilers and microprocessors, to minimize formattransformations to be made by applications.

[0214] The selected formats are defined in the coding rule illustratedin table 3 at the end of the description.

[0215] 3) Data Grouping

[0216] The Ethernet protocol is particularly efficient when transmittedinformation is relatively long. Therefore, it is very advantageous togroup data to that they can be sent all at once to facilitate coherenceand integrity.

[0217] The data grouping criteria may be as follows:

[0218] same transfer mode

[0219] same refreshment period

[0220] functional affinity

[0221] same management of functional validity.

Network Design and Sizing Procedure

[0222] It is essential to define the subscriber hardware and softwarearchitecture, at least from the communication point of view, beforecarrying out a network design and sizing procedure.

[0223] This involves a system and network architecture design phase thatmust clearly identify:

[0224] physically interfaced equipment on the bus, apart fromredundancy,

[0225] transmission and reception subscriber applications seen by thenetwork,

[0226] virtual links as entirely separate elements of the networkarchitecture with its topology.

[0227] The systems must take account of tests and if necessary definespecific virtual links for transferring data to test instrumentationmeans.

[0228] For each hardware equipment, the following are necessary:

[0229] its identification: module name or equipment name,

[0230] its position in the aircraft architecture.

[0231] The following are necessary for each subscriber application:

[0232] its identification: function name,

[0233] its description: a comment,

[0234] its “mapping” on the hardware equipment in the aircraftarchitecture,

[0235] the identification of the logical interface.

[0236] Equipment, even equipment external to the aircraft, or a testinstallation, etc., may support several subscribers each with one orseveral logical interfaces to one or several sub-networks.

[0237] The following are necessary for each virtual link:

[0238] its identification: name of the virtual link,

[0239] the type of information transmitted in the form of a comment,

[0240] the name of the transmitting application,

[0241] the names of receiving applications,

[0242] its routing on hardware equipment in the aircraft architecture inthe form of a list of switches passed through, as identified in thearchitecture,

[0243] the useful passband (bits/s),

[0244] the packet size: the packet size may be fixed or variable in avirtual link, and the maximum size must be given,

[0245] the time IPT,

[0246] justification of the passband, the packet size and the time IPT,

[0247] the usage mode: for “queuing” mode, it is possible to specify ifthe packet size is greater than 482 bytes,

[0248] the maximum latency.

[0249] The transmission system is responsible for defining virtuallinks. The transmission system must make sure that equipment inreception take account of virtual links.

Means Used

[0250] A database supports this part of the process and defines:

[0251] the hardware architecture of the system with all resources andwiring,

[0252] subscribers (components) and their “mapping” on the hardwarearchitecture,

[0253] virtual links of the system and their routings.

Embodiment of a Communication Stack in an Equipment

[0254] This type of stack must enable every subscriber to interface withthe communication network.

[0255] There are three possible approaches for integration of thisfunction in the subscriber equipment:

[0256] an autonomous board satisfying all communication needs andcapable of interfacing with the rest of the equipment simply through abus,

[0257] a list of necessary components and the software that can beintegrated into the target equipment,

[0258] a subscriber interoperability specification with its validationplan in order to check that the supplier's development is conform withthe specified functional requirements. TABLE 1 Number of Number ofSubscriber virtual links Virtual links Class in transmission inreception Large consumer 32 128 Medium consumer 16 64 Small consumer 832

[0259] TABLE 2 Useful Real passband on the network Byte 16 32 64 128(to) 1 ms 2 ms 4 ms 8 ms ms ms ms ms 16 672 336 168 000 84 42 21 10 8280 000 000 000 000 000 500 98 1 328 664 332 000 166 83 41 20 10 000 000000 000 500 750 375 226 2 352 1 176 588 000 294 147 73 36 18 000 000 000000 5000 750 375 482 4 400 2 200 1 550 275 137 68 34 000 000 100000 000000 500 750 375 #Ethernet header − 28 Ots_(UDP/IP header) − 2Ots_(Redundancy field)

[0260] TABLE 3 Type Standard format Character Signed 8-bit ASCIIcharacter (Arinc 653) Integer Signed 32-bit integer (Arinc 653) Unsignedinteger Unsigned 32-bit integer (Arinc 653) Boolean Unsigned 32-bitinteger with info in LSB Real 32-bit floating point integer according toIEEE 303 Propietary type Format not managed bu IOF's

[0261] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

1. Switched full-duplex Ethernet type communication network comprising:at least one source subscriber equipment and at least one destinationsubscriber equipment connected to each other through at least onephysical link through at least one switch and through at least onevirtual link, which is a conceptual representation of a link from asource equipment to at least one destination equipment, wherein eachsource equipment that transmits Ethernet frames comprises: a control tosegregate between virtual links and to allocate a passband for eachvirtual link; and a control to multiplex the virtual links on thephysical links output from the equipment, each transmitted frame havinga field that identifies the virtual link to which it belongs.
 2. Networkaccording to claim 1, wherein each destination equipment comprises acontrol to subscribe in reception to at least one virtual link and tomake segregation between virtual links as far as an application. 3.Network according to claim 1, wherein each switch comprises a control tocontrol an incoming passband for each virtual link.
 4. Network accordingto claim 3, further comprising a static configuration table allowingeach switch to know the virtual links that it has to switch and a numberof authorized packets for a virtual link.
 5. Network according to claim4, wherein each switch comprises: a control to configure each input portseparately to indicate output ports to which each Ethernet frame must bedirected as a function of the field identifier of the virtual link; acontrol to monitor flow of Ethernet frames associated with each virtuallink that passes through the switch; a control to reformat the flow ineach virtual link; and a control to multiplex flows in virtual links oneach output port.
 6. Network according to claim 5, wherein each switchcomprises the following in sequence: an input port; a flow controller; aswitching motor supporting multidestination transfers; a flowcontroller; a flow reformatting device; a virtual link multiplexer; andan output port;
 7. Network according to claim 1, wherein a virtual linkis characterized by: a transfer direction, the virtual link being singledirectional; a source equipment; one or several destination equipment; afixed passband; a guaranteed maximum time for transfer of packets from asource equipment to a destination equipment, regardless of the behaviourof the rest of the network, each virtual link having its own transfertime; a fixed path on the network; and an unique identifier.
 8. Networkaccording to claim 1, wherein network redundancy is achieved by doublingup the network, each subscriber having a connection to each of the twonetworks.